A standard drill chuck that is rotated about an axis of a drill spindle to rotate a drill bit about the axis has a chuck body secured to the spindle and formed centered on the axis with a screwthread. An adjustment sleeve rotatable but axially nondisplaceable on the chuck body is formed angularly equispaced about the axis with a plurality of angled jaw guides. Alternatively it is possible to form the guides on the chuck body and the screwthread on the sleeve for the same effect. Respective jaws in the guides have racks that mesh with the screwthread so that rotation of the sleeve body on the chuck body about the axis in a tightening direction moves the jaws radially together and opposite rotation in a loosening direction moves the jaws radially apart.
It is known from German patent document 3,809,316 to form a window in the sleeve and to provide one of the jaws with an indicator or pointer that is visible through this window so that the user can see the position the chuck is in. The pointer can move relative to a scale indicating the diameter of the drill bit held in the chuck.
Such an arrangement can only be used in a particularly constructed chuck, that is the chuck must be of nonstandard construction to carry the necessary indicator which may be formed as a spreadable ring engaged around the rear ends of all the jaws. In addition this type of arrangement is not readily adaptable to a remote position reader or detector.